Susceptibility Of Conduction Electrons Research Articles

Controlling 4f antiferromagnetic dynamics via itinerant electronic susceptibility

Optical manipulation of magnetism holds promise for future ultrafast spintronics, especially with lanthanides and their huge, localized 4f magnetic moments. These moments interact indirectly by spin polarizing the conduction electrons (the Ruderman-Kittel-Kasuya-Yosida exchange interaction), influenced by interatomic orbital overlap, and the conduction electron's susceptibility around the Fermi level. Here, we study this influence in a series of 4f antiferromagnets, GdT2Si2 (T = Co, Rh, Ir), using ultrafast resonant x-ray diffraction. We observe a twofold increase in the ultrafast intersublattice angular momentum transfer rate between the materials, originating from modifications in the conduction electron susceptibility, as confirmed by first-principles calculations. Published by the American Physical Society 2024

Susceptibility of Conduction Electrons Interacting with Crystal Field States

Susceptibility of Conduction Electrons Interacting with Crystal Field States

The discovery and demonstration of dynamic nuclear polarization—a personal and historical account

The paper gives some background about prewar studies of paramagnetic relaxation, the author's postwar measurements of paramagnetic relaxation using 3 cm microwaves, the beginning studies of alkali metal NMR at Illinois, Overhauser's arrival and proposal, the discovery of the ESR of conduction electrons, the experiment confirming his idea in Li and Na metals, then in solutions of Na atoms in liquid ammonia, and the realization that a form of Overhauser effect might be seen when several isotopes were present in cases where atoms were mobile. Two other experiments at Illinois inspired by the Overhauser experiments are briefly described: measurement of the spin susceptibility of conduction electrons and measurement of spin-lattice relaxation times in superconductors.

Electronically driven instabilities in metals

Electronically driven instabilities of the conduction electrons in metals are manifested as spin density waves, charge density waves accompanied by periodic lattice distortions, or in structural phase transformations and are thought to result from a divergence in X(q). the generalized static electronic susceptibility. Examples of these instabilities are discussed by means of accurate calculations of the noninteraction conduction electron susceptibility X(q) using results of energy-band calculations and our recently developed analytic tetrahedron linear energy method, notably, the occurrence of change density waves in the layered dichalcogenides and the body-centered cubic to omega phase transformation in metals like Zr.

Anisotropic magnetic, electrical, and thermal transport properties of the Y-Al-Ni-Co decagonal approximant

We have investigated anisotropic physical properties (magnetic susceptibility, electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of Y-Al-Ni-Co decagonal approximant with composition ${\text{Al}}_{76}{\text{Co}}_{22}{\text{Ni}}_{2}$. The crystalline-direction-dependent measurements were performed along three orthogonal directions ${a}^{\ensuremath{\ast}}$, $b$, and $c$ of the Y-Al-Ni-Co unit cell, where $(a,c)$ monoclinic atomic planes are stacked along the perpendicular $b$ direction. Anisotropic magnetic susceptibility of conduction electrons is paramagnetic for the field lying within the $(a,c)$ atomic planes and diamagnetic for the field along the $b$ direction. Anisotropic electrical resistivity is low in all crystalline directions, appearing in the order ${\ensuremath{\rho}}_{{a}^{\ensuremath{\ast}}}g{\ensuremath{\rho}}_{c}⪢{\ensuremath{\rho}}_{b}$. Thermopower shows electron-phonon enhancement effect. Anisotropic bare thermopower (in the absence of electron-phonon interactions) was extracted, appearing in the same order as the resistivity, $|{S}_{{a}^{\ensuremath{\ast}}}^{\text{bare}}/T|g|{S}_{c}^{\text{bare}}/T|g|{S}_{b}^{\text{bare}}/T|$. Anisotropic thermal conductivity appears in the order ${\ensuremath{\kappa}}^{b}g{\ensuremath{\kappa}}^{c}g{\ensuremath{\kappa}}^{{a}^{\ensuremath{\ast}}}$, so that $b$ is the most conducting direction for both electricity and heat. Hall coefficient ${R}_{H}$ exhibits pronounced anisotropy, where the magnetic field in a given crystalline direction yields the same ${R}_{H}$ for the current along the other two crystalline directions in the perpendicular plane. These anisotropies are analyzed in terms of the anisotropic structure of the Y-Al-Ni-Co phase and the ab initio calculated anisotropic Fermi surface. The results are compared with the literature-reported anisotropy of the physical properties of the $d$-Al-Ni-Co decagonal quasicrystal.

Magnetic properties of transition-metal nanoclusters on a biological substrate

We have investigated the magnetic properties of transition-metal clusters with a single grain size of about 1 nm. These metallic nanoclusters have been deposed on a biological substrate. This substrate is a purified self-assembling paracrystalline surface layer (S-layer) of the Bacillus sphaericus strain JG-A12, which exhibits square symmetry and is composed of identical protein monomers. First data of the magnetic susceptibility, taken in a SQUID magnetometer at 0< B<7 T and 1.8 K< T<400 K, reveal unusual magnetic properties. The Stoner enhancement factor of the d conduction-electron susceptibility in the Pd and Pt nanoclusters is dramatically reduced compared to the one of the corresponding bulk transition metals. The weakened magnetism of the 5d electrons is considered to play a crucial role for the occurrence of superconductivity in microgranular Pt by adjusting the balance between electron–phonon interactions and competing magnetic interactions.

Magnetic properties of amorphous, crystalline, and liquid Ni-B alloys

From a comprehensive study of the magnetic properties of amorphous and liquid ${\mathrm{Ni}}_{100\ensuremath{-}x}{\mathrm{B}}_{x}$ alloys with $18.5&lt;~x&lt;~40,$ the individual contributions to the magnetization are identified and determined separately. The matrix of the amorphous Ni-B alloys is found to exhibit Pauli paramagnetism even for $x=18.5,$ where the observed magnetization was dominated by superparamagnetic particles. The Pauli susceptibility decreases monotonically with increasing B-content and, for a given composition, it agrees well with extrapolated room-temperature liquid state data and with the value of the corresponding crystalline stoichiometric compound. The critical concentration for the onset of spontaneous magnetic order is established to be more than 81.5-at. % Ni. On the basis of the electronic density of states (DOS) deduced from previous low-temperature specific-heat measurements for various Ni-metalloid alloys, the Stoner-enhanced Pauli susceptibility is calculated for the Ni-B system and a good agreement with the experimental conduction electron susceptibility is obtained. The temperature dependence of the Pauli susceptibility is also discussed for amorphous Ni-B alloys and for liquid Ni-metalloid alloys, the features being explained in terms of the DOS data.

The magnetic structures of holmium-yttrium superlattices in an applied magnetic field

The magnetic structures of a rare earth superlattice in an applied magnetic field have been determined using neutron scattering techniques. The sample was grown using the LaMBE facility in Oxford and the periodic unit consisted of 41 planes of holmium and 16 planes of yttrium. The results showed four different types of magnetic phase corresponding to the helix, helifan, fan and ferromagnetic phases observed when a magnetic field is applied in the basal plane of bulk holmium. In the superlattice the correlation length was very long for the ferromagnetic phase, about 10 superlattice periods for the helix, about 4 superlattice periods for the fan and there was little, if any, correlation between the superlattice blocks for the helifan phase. The structures depended in detail upon the history in field and temperature as the configuration was approached. The most striking aspect of the result is that the helical phase is stable to higher fields in the superlattice than in the bulk. It is argued that this is because the conduction electron susceptibility in yttrium favours a modulated structure more strongly than in holmium and that the propagation of conduction electrons throughout the superlattice transfers this enhancement to the holmium blocks.

Metal-insulator transition inRbC60polymer fulleride studied by ESR and electron-spin relaxation

The ESR intensity, line shape, and longitudinal electron-spin relaxation in the polymer phase of the ${\mathrm{RbC}}_{60}$ fulleride are investigated in the temperature range $4.2&lt;T&lt;300 \mathrm{K}.$ Most attention is focused on the metal-insulator transition region (25--50 K). It is found that below 50 K the ESR line can be separated into two Lorentzian components ascribed to conduction electrons and some localized paramagnetic centers (with concentration of about 0.03 per formula unit) with allowance made for the relaxation bottleneck. The decrease of the conduction-electron susceptibility obeys an activation law with the characteristic energy $\ensuremath{\Delta}{/k}_{B}=80\ifmmode\pm\else\textpm\fi{}10 \mathrm{K}$ related to the opening of a gap $2\ensuremath{\Delta}\ensuremath{\approx}100 {\mathrm{cm}\mathrm{}}^{\mathrm{\ensuremath{-}}1}.$ The same quantity is found by analyzing both longitudinal and transverse relaxation caused by fluctuations of internal fields with correlation time ${\ensuremath{\tau}}_{c}\ensuremath{\propto}\mathrm{exp}(2\ensuremath{\Delta}{/k}_{B}T).$ Below 25 K, the temperature dependencies of the linewidth and the relaxation times change abruptly, revealing the development of a new ordered state. The nature of this state is discussed.

Magnetism of (Gd1−xYx)2In

Magnetic susceptibility and electrical resistivity of the (Gd1−xYx)2In system (for x ⩽ 0.5) were investigated in a wide temperature range. For high temperatures (300–800 K) the magnetic susceptibility does not obey the Curie-Weiss law and may be fitted either by the sum of the Curie-Weiss term and a large negative, temperature-independent term or by an expression which includes temperature variation of the conduction electron susceptibility. This susceptibility is assigned to the Gd 5d electrons. Interaction between 4f moments via 5d band is discussed as a possible reason for the occurrence of the temperature-induced metamagnetic transition observed for x ⩽ 0.15. The dominant role of the 5d electrons in magnetic interactions is supported by a theoretical and experimental determination of the electronic structure of Gd2In.

Structural and magnetic properties of holmium-scandium alloys and superlattices

The properties of Ho-Sc alloys and superlattices grown by molecular-beam epitaxy have been investigated using x-ray and neutron-diffraction techniques. Structural studies reveal that the alloy samples have different a lattice parameters for the Sc-seed layer and the Ho:Sc alloy grown on top of the seed layer; while the superlattices have different a lattice parameters for the Sc seed, and for both the Ho and Sc in the superlattice layers. The structural characteristics are related to the large lattice mismatches (of the order 7{percent}) between the constituent elements. The magnetic moments in the alloys form a basal-plane helix at all temperatures, with distortions of the helical arrangement for samples with the highest Ho concentrations. The dependences of the N{acute e}el temperature, T{sub N}, and the helical wave vector upon both temperature and concentration are compared with those of other alloy systems. It is found that a good description of the dependence of T{sub N} upon concentration is given by a virtual-crystal model where the peak in the conduction-electron susceptibility varies linearly between that of the pure constituents. In the superlattices, the moments also form a basal-plane helix at T{sub N}. In this helical phase, some samples exhibit a short-range coherence ofmore » an antiferromagnetic coupling between adjacent Ho blocks. For one superlattice, there is a low-temperature transition to a ferromagnetic phase, in which moments are ferromagnetically aligned within Ho blocks, and coupled antiferromagnetically between adjacent Ho blocks. The contrast with systems which have Y or Lu as the nonmagnetic element is discussed in terms of the structural properties of the samples, band-structure calculations, and the possible influence of dipolar forces. {copyright} {ital 1997} {ital The American Physical Society}« less

Interaction between localized and conduction-electron spins in the high-Tc superconductor Gd:EuBa2Cu3O6+x.

This work studies the spin-spin interaction between the conduction electrons and localized spins in high-${\mathit{T}}_{\mathit{c}}$ superconductors. We report the ESR at 9.74 GHz of low concentration of Gd substituting the Eu in single crystals of ${\mathrm{EuBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ (x\ensuremath{\approxeq}0.85). At low temperatures just above ${\mathit{T}}_{\mathit{c}}$, the Gd ESR spectra in the c axis direction is almost resolved. With increasing temperature, exchange effects narrow most of the spectrum into a line close to g=2.00 except the 7/2\ensuremath{\leftrightarrows}5/2 transition, which remains partially resolved. This transition has a Dysonian line shape and shows a Korringa behavior. The narrowing of the spectra and the Korringa behavior indicate an exchange coupling between the conduction electrons and the Gd spin systems, and can be analyzed by the Barnes-Plefka theory. From the linewidth broadening of the 7/2\ensuremath{\leftrightarrows}5/2 transition and the Barnes-Plefka theory we obtain a Korringa constant \ensuremath{\Delta}${\mathit{H}}_{\mathit{K}}$/T=0.5 G/K. From this value we calculated the exchange interaction ${\mathit{J}}_{\mathit{Ss}}$ between the Gd spins, S, and the conduction electrons, s, using reported values for conduction electron susceptibility. We obtain ${\mathit{J}}_{\mathit{Ss}}$=0.5\ifmmode\pm\else\textpm\fi{}0.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ eV, a value that is two or three orders of magnitude smaller than those observed in metals. It explains the small effect of magnetic ions on the ${\mathit{T}}_{\mathit{c}}$ in the R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ compounds. (R = rare earth). From the angular dependent spectra of Gd:${\mathrm{EuBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ we obtain zero field terms of ${\mathit{b}}_{2}^{0}$=-1800 MHz, ${\mathit{b}}_{4}^{0}$=-180 MHz, and ${\mathit{b}}_{4}^{4}$=+600 MHz. These values are not significantly different from those obtained for Gd in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$. \textcopyright{} 1996 The American Physical Society.

Magnetic structures of holmium-lutetium alloys and superlattices.

Alloys and superlattices of Ho and Lu have been grown using molecular beam epitaxy and their magnetic structures determined using neutron-scattering techniques. The 4f moments in the alloys form a helix at all compositions with the moments aligned in the basal plane perpendicular to the wave vector, q, of the helix. The dependence of both the transition temperature, ${\mathit{T}}_{\mathit{N}}$, and q on composition are consistent with a model where the conduction-electron susceptibility is the weighted average of the constituents. Below ${\mathit{T}}_{\mathit{N}}$ the superlattices also order into helical structures, with the phase of the helix remaining coherent through the nonmagnetic Lu blocks. The neutron scattering from the superlattices is consistent with a model in which there are different phase advances of the helix turn angle through the Ho and Lu blocks, but with a localized moment on the Ho sites only. A comparison of the parameters extracted from this modeling with earlier results for Ho/Y superlattices reveals several trends and suggests that the propagation of coherent magnetic order in these materials may depend on the band structure of the superlattice as a whole and cannot be explained in terms of independent blocks of Ho and Lu. At low temperatures, for superlattices with fewer than approximately twenty atomic planes of Ho, the Ho moments within a block undergo a phase transition from helical to ferromagnetic order, with the coupling between successive blocks dependent on the thickness of the Lu spacer. \textcopyright{} 1996 The American Physical Society.

Pairing mechanism mediated by crystal-field excitation in van Vleck paramagnetic metals

We have shown so far that in van Vleck paramagnetic metals such as Pr indirect electron-electron interaction arises from virtual excitation of the crystal field singlet ground state. This effective interaction turns repulsive near the Fermi surface. We study the possible pairing mediated by the spin-fluctuation due to this repulsie interaction. For the conduction band where the conduction electron susceptibility takes a maximum at q=0, formal discussion can be made in parallel with the superfluidity in 3He. Among the spin triplet pairings crystal field anisotropy selects the most favorable state.

ATOMIC SHORT RANGE ORDER AND SPIN DENSITY WAVE PROPAGATION IN CuMn

Neutron scattering studies of the atomic short range order (ASRO) and spin density waves (SDW) were carried out for a Cu-35% Mn sample with an unusually high degree of ASRO that develops mostly in a single tetragonal domain. The SDW peaks show a distinctly non-cubic distribution that is readily correlated with the ASRO and which corresponds to the propagation of SDW only in the c plane of the tetragonally based ASRO. The high degree of ASRO and single domain character of this carefully heat-treated sample produces an unusually stable SDW with a higher transition temperature and a larger correlation length than is observed for quenched alloys of the same Mn content. Since SDW stability depends on structural features in the conduction electron susceptibility and on flat, parallel sections of the Fermi surface, these observations suggest that the degree of ASRO and/or the presence of single domain ASRO influences the sharpness of the relevant Fermi surface features in these alloys.

Monte Carlo computations of the magnetic susceptibility of conduction electrons in a model of disordered semiconductors

Monte Carlo computations of the magnetic susceptibility of conduction electrons in a model of disordered semiconductors

Magnetic studies of amorphous NiP alloys

Magnetization studies were performed on amorphous Ni 100− x P x alloys with 15 ≤ x ≤ 23 in the temperature range from 4.2 to 300 K and in fields up to 9 kOe. Samples with x < 17 were prepared by electrodeposition, whereas samples with x ≥ 17 were obtained by either electrodeposition or melt-quenching. The conduction electron susceptibility of the latter samples showed to be independent of the preparation method. Furthermore, the magnetic behaviour was found to differ strongly for x ≤ 17 and x ≥ 17. These different magnetic properties are attributed to a change in the size and behaviour of the magnetic inhomogeneities embedded in the NiP matrix: for x ≥ 17, they can be described as giant-moment paramagnetic clusters, whereas for x ≤ 17 they form superparamagnetic particles.

Possible temperature dependence of the orbital susceptibility of C 24SbCl 5 at low temperatures

Magnetic susceptibility {ie885-1} and {ie885-2} were measured in the second stage SbCl5 graphite intercalation compound (C24SbCl5). {ie885-3} and {ie885-4} revealed the Curie-Weiss type paramagnetic deviation at low temperatures. {ie885-5} is diamagnetic and increases in magnitude with the decrease of temperature approximately below 40K. There exists no anisotropy of g-value in C24SbCl5. These facts suggest that the orbital susceptibility of conduction electrons in the graphitic π band of C24SbCl5 has the temperature dependence at low temperatures.

Susceptibility of Conduction Electrons Interacting with Crystal Field States

Susceptibility of Conduction Electrons Interacting with Crystal Field States

Theory of electron-phonon interaction effects on the spin susceptibility of conduction electrons

A theory of the spin susceptibility of conduction electrons is derived using a temperature Green function formalism in the presence of an electron-phonon interaction. It has been shown that the modifications to the spin susceptibility brought about by considering the magnetic field dependence of the electron self-energy are cancelled by the mass enhancement due to the electron-phonon interaction. However, by considering both the electron-electron and electron-phonon interactions the authors show that the exchange enhancement parameter ( alpha ) due to the electron-electron interaction changes to alpha (1+ gamma )-1 where gamma is the electron-phonon mass enhancement parameter. In view of the present controversy concerning the role of the electron-phonon interaction in the magnetism of solids, their work is expected to pave the way for a better quantitative understanding of the effect.